Effects of converting enzyme inhibition on baroreflex sensitivity in patients with myocardial infarction.

BACKGROUND. Baroreflex sensitivity provides useful prognostic information in patients after acute myocardial infarction. However, no data are available about the effects of converting enzyme inhibition on this variable. OBJECTIVES. The aim of the study was to evaluate the effects of angiotensin-converting enzyme inhibition on baroreflex sensitivity in patients after uncomplicated myocardial infarction. METHODS. Twenty-five patients after uncomplicated myocardial infarction underwent baroreflex sensitivity evaluation 72 to 96 h after symptom onset and after 4 days of captopril therapy. Twenty additional patients with the same characteristics were evaluated at the same time intervals before and after placebo administration to identify spontaneous baroreflex sensitivity variations. Baroreflex sensitivity was assessed by calculating the regression line relating phenylephrine-induced increases in systolic blood pressure to the attendant changes in the RR interval. RESULTS. The mean baroreflex sensitivity value increased after captopril administration from 6.5 +/- 4.2 to 11.8 +/- 6.1 ms/mm Hg (p less than 0.01) and in individual analyses increased by greater than 2 ms/mm Hg in 68% of patients. Mean plasma renin activity increased after captopril from 3.7 +/- 2.4 to 8.5 +/- 4.9 ng/ml per h (p less than 0.005). No difference was detectable in baroreflex sensitivity and plasma renin activity values according to the site of necrosis. In the control group, baroreflex sensitivity and plasma renin activity remained unchanged between the two studies. CONCLUSIONS. This study demonstrates that in patients with uncomplicated myocardial infarction, captopril significantly improves the chronotropic response to baroreceptor stimulation.